Sunday, July 16, 2017

How do we construct a unified self-identity as a thinking and feeling person inhabiting a body, separate and unique from other entities? A “self” with the capacity for autobiographical memory and complex thought? Traditionally, the field of cognitive science has been concerned with explaining the mind in isolation from the body.

The growing field of embodied cognition, on the other hand, seeks to rejoin them. One major strand has focused on grounding higher-order semantics and language understanding in perceptual and sensory-motor representations. This view is distinct from theories of knowledge based on abstract, amodal representations divorced from sensory-motor experience. Another wing of the embodied approach is concerned with how interoception— the inner sense of your physical state — grounds your feelings and emotions in the body. Interoceptive awareness of visceral functions such as heartbeat has been related to core consciousness and awareness of self, including body image.

A relatively neglected yet critical aspect of any grand theory of the embodied self is the vestibular system. The vestibular system is the set of sensory organs responsible for maintaining our balance and keeping our visual field in a stable position while our head moves around. These organs are located in the inner ear and include...

...two otolith organs (the saccule and utricle), which sense linear acceleration (i.e., gravity and translational movements), and the three semicircular canals, which sense angular acceleration in three planes. The receptor cells of the otoliths and semicircular canals send signals through the vestibular nerve fibers to the neural structures that control eye movements, posture, and balance.

We take the vestibular system for granted until something goes wrong, like motion sickness (a mismatch of movement perceived by the vestibular and visual systems) or a rare disorder of the inner ear such as Menière’s disease. But how can a dysfunction of the inner ear influence our sense of self?

Derealization: "Experiences of unreality or detachment with respect to surroundings (e.g., individuals or objects are experienced as unreal, dreamlike, foggy, lifeless, or visually distorted."

Beyond the expected high frequency of dizziness, the patients were much more likely to experience feelings of Shifting Ground, Spaced Out, Body Feels Strange, and Not Being in Control of Self than were controls (see bottom half of the figure below).

The authors suggest that abnormal vestibular signals disrupt the relationship of the self to the environment, leading to strange feelings of detachment:

Vestibular disease causes primary symptoms of vertigo and feelings that the ground is unstable ... which are more marked in distinct, acute episodes. These immediate symptoms are, by definition, unreal experiences since the body is not spinning and the ground is not heaving, but they are readily understandable as perceptions derived directly from abnormal sensory signals. Vestibular dysfunction could also compromise more general precepts of stable relationships between the self and the environment...

Symptoms of depersonalization/derealization can be induced experimentally in healthy people via caloric stimulation. This procedure is used medically to check the vestibulo-ocular reflex, which stabilizes the visual image while the head is moving. The test involves delivering warm or cold water into the ear canal and observing the resultant eye movements (or lack thereof).

Song et al. (2008) administered caloric stimulation to 20 of their vestibular patients and 20 controls. After stimulation, many healthy participants reported feelings of detachment/separation from their surroundings (40%), and that their body feels strange/different (50%). These were novel experiences for most. Conversely, the patients reported no such changes after stimulation because they already experience these symptoms.

A recent study subjected 100 healthy participants to unilateral centrifugation to stimulate the utricles (Aranda-Moreno & Jáuregui-Renaud, 2016). The target of this test differs from the caloric procedure, which stimulates the semicircular canals. The utricles and the semicircular canals detect different types of motion (linear acceleration and angular acceleration, respectively), and the authors wanted to see if unilateral centrifugation would produce the same effects as caloric stimulation. And indeed, after centrifugation, symptoms of depersonalization and derealization were reported with increased frequency — e.g., Surroundings seem strange and unreal; Time seems to pass very slowly; Body feels strange or different in some way (see Table below for details).

These results provide further evidence that the vestibular system contributes to the construction of the self. The sense of inhabiting one's body is assembled from many different inputs, of course. These can go awry in epilepsy, migraine, focal brain injury, psychiatric disturbances, and under extreme stress. Although rare, out-of-body experiences are more frequent in persons who suffer from dizziness due to vestibular disorders (Lopez & Elzière, 2017). In these instances, the vestibular system is unable to ground the self within the body.

About Me

Born in West Virginia in 1980, The Neurocritic embarked upon a roadtrip across America at the age of thirteen with his mother. She abandoned him when they reached San Francisco and The Neurocritic descended into a spiral of drug abuse and prostitution. At fifteen, The Neurocritic's psychiatrist encouraged him to start writing as a form of therapy.